Membranological properties of tactic poly(2-hydroxyethyl methacrylate)s

Abstract

Two series of membranes of various degree of hydration have been prepared by postcrosslinking highly syndiotactic and isotactic poly 2-hydroxyethyl methacrylate, P(HEMA) with various amounts of hexamethylene diisocyanate(HMDIC). The equilibrium water content, the partition coefficient and the permeability of the model solutes such as urea, acetamide, NaCl, 2-propanol, and iso-butanol for these membranes were measured. In addition, differential scanning calorimetry(DSC) study for the membranes was performed. The membranes of the isotactic precursor are more hydrated at 25℃ compared to the ones of its syndiotactic counterpart. This may be due to the more hydrophobic nature of syndiotactic P (HEMA). The partition coefficient data show that the solutes of urea, acetamide, and NaCl are partitioned only into the water containing region, whereas the alcohol solutes are preferentially sorbed on to polymer matrix. The permselectivity data of urea to NaCl reveal that the permselectivity of crosslinked isotactic P (HEMA), (ISO) membranes increases as the amount of HMDIC is increased from 2.5 to 10 mole %, while the trend is reversed for crosslinked syndiotactic P (HEMA), (SYN) membranes. The apparent diffusivity order of urea, acetamide, and NaCl is not the same in those two characteristic membranes: the order is $urea > NaCl > acetamide$ for highly crosslinked ISO membranes, and $NaCl>urea>acetamide$ for all SYN membranes, which was compared with the free diffusion data in aqueous solution and interpreted in terms of the water structural orderliness within membranes. The temperature dependence of permeability through uncrosslinked highly syndiotactic P(HEMA) membrane is also reported for highly polar organic solutes such as ureas, methyl substituted ureas and amides, and for NaCl and $Na_2SO_4$. The membranes used was equilibrated in distilled water at each temperature before measurements. From the linear correlationship between the excess heat capacities, $ΦC}_p^o$ (ex...